Apparatus for the manufacture of sulfur dioxide from sulfates



-April 14, 1964 H. ZIRNGIBL 3,129,063

APPARATUS FOR THE MANUFACTURE OF SULFUR DIOXIDE FROM sULFATEs OriginalFiled March 28-, 1957 2 Sheets-Sheet 1 INVENTOR HANS ZIRNGIBL ATTORNEYApril 1964 H. ZIRNGIBL 3,129,063

APPARATUS FOR THE MANUFACTURE OF SULFUR DIOXIDE FROM SULFATES OriginalFiled March 28, 1957 2 Sheets-Sheet 2 INVENTOR HANS ZIRNGIBL ATTORNEY3,129,063 Patented Apr. 14, 1964 3,129,063 APPARATUS FOR THE MANUFACTUREOF SULFUR DIOXIDE FROM SULFATES Hans Zirngibl, Leverkusen-liayerwerk,Germany, asslgnor to Farbenfabriken Bayer Aktiengesellschaft,Leverkusen, Germany, a corporation of Germany Original application Mar.28, 1957, Ser. No. 649,032. Divided and this application Jan. 25, 1969,Ser. No. 4,287 Claims priority, application Germany Mar. 31, 1956 4Claims. (Cl. 23-262) The instant invention relates to a process for theproduction of sulfur dioxide from sulfates and to \an apparatus forcarrying out such process and is a division of application Serial No.649,032, filed March 28, 1957, now abandoned.

The production of sulfur dioxide by decomposition of sulfates hasalready been repeatedly described. When decomposition by reduction iscarried out on a technical scale, however, there is a danger of thesulfates not being completely reduced when part of the reducing agent islost in the furnace atmosphere due to combustion. On the other hand, ifexcess reducing agent is supplied, sulfides can remain in the residueand these sulfides would be a nuisance in the further processing of the,residue. In addition, undesirable reduction products are formedprimarily sulfur vapours, which have to be burnt off before the sulfurdioxide can be used for the manufacture of sulfuric acid.

Processes and apparatus have already been proposed for the purpose ofovercoming these difiiculties. It is, for example, possible to use aninternally heated rotary kiln into which air is injected at variouspoints. At the same time, the interior of the rotary kiln is formed intodifferent zones in which there are differing tempenatures and alsodifferent compositions of the gas atmosphere and reaction material. Airis injected at 700 800" C. in an initial zone, whereby the sulfurvapours and other undesirable reduction products issuing from theadjacent, hotter zone are burnt without the reduction coke added to thesulfates being attacked at this temperature. In this zone, the reactionmaterial is incompletely reduced at temperatures up to 1100 C. with lessthan the stoichiometric amount of solid or gaseous reducing agents. Thefractions which so far have not been reduced are reacted in the hottest,final zone with gaseous reducing agents. Even this process still shows acertain number of defects, particularly when it is used on a largetechnical scale. It is certainly true that the required relativeadjustment of the zones can be carried out in the gas atmosphere, butthis adjustment cannot be carried out in the reaction material.Furthermore, the injection of air (the various zones are arranged byregulating the supply of air) into the hotter parts of the rotary kilnmeets with technical difiiculties. The necessary high temperatures leadto frequent breakdowns, which are caused by the formation of rings andother deposits and also damage to the masonry. This is particularly thecase when mixtures are to be fired which have melting points andsintering points which are very close to one another.

It has now been found that the difficulties described above can beavoided, and satisfactory decomposition products can be obtained, if thereduction of sulfates is carried out in three stages, the atmosphere inthe first stage, i.e., in the coldest zone, being kept slightlyoxidizing the atmosphere in the middle zone being kept inert, whenreduction carbon is used and employing in the third zone and final stagea reducing action. It is, however, also possible to operate with areducing gas atmosphere in both of the last zones. The decomposition iscarried out on a conveying belt which is equipped with a hood-heatingsystem which permits the supply of heat in the three zones. Thoseexhaust gases from the final, hottest zone and from the adjacent,slightly less hot middle zone which are not required for temperaturecontrol, and consequently are not recycled, are introduced into a colderzone, if desired with the addition of air and perhaps with supplementaryheating. The reduction takes place mainly in the middle zone, whichcontains less than the stoichiometric amount of reducing agent. Thereaction material is prefenably heated in the initial zone to 500-800C., in the middle zone to 900-1200 C. and in the final zone up tosintering temperature of the material used, i.e., about 1100 C. to about1400 C.

The process is indicated diagrammatically in FIG. 1 of the accompanyingdrawings. The reaction material is first of all granulated in agranulating device a and initially dried in a hopper b. It then passeson to a conveyor belt d, which conveys the material successively intothe separate heating zones of the hood-heating system. In a heatingarrangement 0, fuel, for example oil, is supplied in the direction ofthe vertical arrows, and air for combustion is supplied through a fan Iin the direction of the horizontal arrow. In the initial zone I, thereaction material is preheated to 500-800 C. The atmosphere ismaintained so as to be slightly oxidizing by the addition of air, butcarbon is not affected at the temperatures prevailing this zone.Consequently, all undesirable reduction products, such as for examplesulfur vapour, which are contained in the gases leaving the middle zoneII at h and entering the initial zone at e by way of a fan 0, arecompletely burnt to form sulfur dioxide. If desired, the exhaust gasescan be additionally heated before they enter the initial zone. Theproduction gas discharging at i through a fan It can therefore be usedfor the manufacture-of sulfuric acid by the catalytic process, afterdust has been extracted in the usual manner from the gas, withoutfurther purification.

The reduction takes place mainly in the middle zone at a temperature of900- 0 C. The amount of reducing agent in this zone is less than thestoichiometric amount. If the reduction taking place in this zone isproduced by solid reduction agents, such as for example carbon, theatmosphere is kept inert. It is however also possible to work withgaseous reducing agents.

The final reduction takes place in the last, hottest zone III, in whichthe material is heated up to sintering temperature. That proportion ofthe exhaust gases which is required for temperature control and whichdischarges at k through a fan m is returned into zone II at g. Theremainder is fed, after supplementary heating, at 1 into the middlezone.

FIG. 2 shows a modification of the above-described process in which theexhaust gases are removed jointly from the middle zone and final zone.That amount thereof which is required for temperature control isreturned into these zones while the remainder is supplied to the initialzone, so that also in this case all the production gas must pass throughthe oxidizing initial zone, where the undesirable reduction products areeliminated," before it is extracted.

The necessary energy for heating and decomposition purposes can beproduced from coal dust or by gas firing or oil firing.

It is particularly advantageous for all or part of the energy to begenerated by the combustion of elementary sulfur. With the process usedherein, a complete combustion of the sulfur is assured. At the sametime, the concentration of sulfur dioxide in the production gases isincreased. This is particularly favorable for the further processing ofthe final gas to form sulfuric acid by the catalytic process since thedimensions of the apparatus can be kept smaller than when dilute gasesare used, owing to the higher sulfur dioxide content.

Occasionally, it is advantageous to use a mixed firing system, whereinother combustible substances containing carbon are added as well thereduction carbon to the reaction material in the middle zones, thesesubstances yielding some of the energy which is required.

An essential advantage of the process is to be seen in the fact that thereaction conditions in the separate zones can be exactly adjusted. Anydesired temperature can be produced without any difficulty in each zonewith a latitude of about C. In addition, the gas composition and gaspressure, as Well as the residence times of the solid phase, can bemodified. Further advantages, consist in the good distribution of thegas in the material under treatment, in the high speed of heat exchangeand in the good utilization of the heat with a low heat drop. By usingthe procedure which is proposed, it is ensured that the production gasis free from undesirable impurities. Moreover, the dust content of theproduction gases is considerably lower than when the rotary kiln processis used. The process according to the invention enables defects to beimmediately detected, examples of these defects being an incorrect rateof introduction of the initial powder, incorrectly measured quantitiesof reducing agents or incorrect adjustment of the gas atmosphere. Owingto the use of the endless conveyor belt, the operation is not stopped bymelting or sintering of the reaction material. Since the process permitsaccurate adjustment of the temperature, it is also possible to burnmixtures which have sintering and melting points closely adjacent to oneanother.

In the decomposition of calcium sulfate with the simultaneous formationof cement clinker, it is for example not necessary to make the finalcomposition of the clinker dependent on the manner in which the furnaceis operated, as was formerly the case. Using the conveyor belt equippedwith a hood heating system, it is possible to obtain completedesulfurization and simultaneously produce special cements, such as forexample aluminate and Ferrari cements and clinkers containing dicalciumsilicate and alumina which may be leached on alumina.

In conjunction with the simultaneous production of sulfuric acid andPortland cements, it has been contended that special cements such asthose referred to above can be obtained by the desulfurization ascarried out in rotary kilns. In practice, however, this has not provedto be the case, the same being prevented by damage to the brickwork andexcessive ring formation.

By using the process of the invention, it is possible to decompose alltechnically important sulfates without any interference, as, for exampleferrous sulfate, magnesium sulfate, calcium sulfate and mixtures ofcalcium sulfate with materials containing clay, in which case cements ofclinkers which can be leached on alumina are simultaneously obtained, aswell as aluminum sulfate, mixtures of aluminum sulfate and sodiumsulfate, sodium sulfate bauxite and other sulfate mixtures.

Example 1 78 parts of anhydride containing 91% of CaSO are mixed with15.2 parts of a clay slate having the following composition:

and 5.5 parts of coke (81% C), ground to the fineness of cement andmoulded in the usual manner with about 1012% of water in a granulatingplate. For the purpose of protecting the grate bars, the conveyor beltis initially covered to a height of 3-5 cm. with finely burnt clinkerand the granules are placed thereon to a height of 50 cm. For protectionagainst heat losses and as a sealing means with respect to the heatinghoods arranged above the conveyor belt, fine-grain or dust-like clinkeris placed at both sides when the band is charged with the granules. Thematerial travels beneath the first hood, where it is initially heated bythe exhaust gases from the second zone to about 600 C. In order toobtain the required oxygen content of 12%, the necessary amount of airis forced into this hood. Thereafter, the material is heated under thesecond hood by gases from the final zone and by additional heating withoil flames to 1000- 1100 C. in an inert gas atmosphere, and finallyunder the last hood by oil flames in a slightly reducing atmosphere to1400 C. The gas atmosphere beneath the hoods is adjusted by regulatingthe amounts of oil and air supplied for combustion. The gas forcombustion is previously forced through the hot clinker on the lastsection of the belt and in this way is heated while simultaneouslycooling the clinker.

The resulting clinker is sintered and practically free from sulfur. Itis mixed in the usual manner with gypsum and crushed to form cement. Thehot gases leaving the kiln, which have a temperature of about 200 C. andcontain sulfur dioxide, are freed from dust, mixed in known manner withair and treated in the presence of catalysts to form sulfuric acid. Thecapacity of the sintering plant is in the region of 7.5 tons per day persquare meter of available sintering area.

Example 2 Ferrous sulfate monohydrate is granulated in admixture withcoke while hot and with a concentrated ferrous sulfate solution, anddecomposed on a conveyor belt with hood heating, substantially asdescribed in Example 1. The exhaust gases from the final zone arehowever extracted jointly with the exhaust gases from the middle zones,as is shown in FIG. 2. The molar ratio between SO zC is 2:1. Thetemperature is kept at 500 C. in the pre-heating zone, 900 C. in thesecond zone and 1100 C. in the last zone.

The capacity is about 6 tons per day per square meter of availablesintering area with a velocity of the conveyor belt of 15 cm./min. and alayer thickness of 20 cm.

Example 3 A mixture of aluminium sulfate/sodium sulfate/coke in themolar ratio of aluminium sulfatezsodium sulfate=1z1 and SO :C=1.6:l isgranulated and burnt as described in Example 1. The temperature isadjusted to 500 C. in the pre-heating zone, 1000-1100 C. in the middlezone and 1200 C. in the final zone. Sodium aluminate is formed whichcontains less than 0.1% of sulfur.

I claim:

1. A device for manufacturing sulfur dioxide by the reduction ofsulfates, comprising an endless conveying belt, three successivelyarranged heating hoods positioned to partially surround the conveyingbelt and to substantially completely surround a portion of belt travel,each of said heating hoods being equipped with a burner in the upperpart thereof above the belt for directing heat downwardly toward saidbelt, a gas inlet for produced reduction gas in the upper part of eachof said hoods above the belt between it and said burner, a gas outletfor produced reduction gas in the lower part of the heating hood belowthe belt, means for dedusting and purifying S0 containing produced gas,gas conduit means connecting said gas outlet of the first heating hood(in the direction of the movement of the conveying belt) to saiddedusting and purifying means, the gas outlets of the second and thirdheating hoods communicating with the produced reduction gas inlets ofthe preceding heating hood, means for introducing S0 containingmaterials to be reduced on to said conveying belt in front of the firstof said hoods for passage on said belt through said hoods, and means forwithdrawing the spent S0 material from the conveying belt behind thelast of said three hoods.

2. A device for manufacturing sulfur dioxide by the reduction ofsulfates, comprising an endless conveying belt, three successivelyarranged heating hoods positioned to partially surround the conveyingbelt and to substantially completely surround a portion of belt travel,each of said heating hoods being equipped with a burner in the upperpart thereof above the belt for directing heat downwardly toward saidbelt, a gas inlet for produced reduction gas in the upper part of eachof said hoods above the belt between it and said burner, a gas outletfor produced reduction gas in the lower part of the heating hood belowthe belt, means for drying S0 containing produced gas containing moistsulfate granules, means for dedusting and purifying S0 containingproduced gas, gas conduit means connecting said gas outlet of the firstheating hood (in the direction of the movement of the conveying belt) tosaid means for drying and dedusting and purifying, the gas outlets ofthe second and third heating hoods communicating with the producedreduction gas inlets of the preceding heating hood, means forintroducing S0 containing material to be reduced on to said conveyingbelt in front of the first of said hoods for passage on said beltthrough said hoods, and means for withdrawing the spent S0 material fromthe conveying belt behind the last of said three hoods.

3. A device for manufacturing sulfur dioxide by the reduction ofsulfates, comprising an endless conveying belt, three successivelyarranged heating hoods positioned to partially surround the conveyingbelt and to substantially completely surround a portion of belt travel,each of said heating hoods being equipped with a burner in the upperpart thereof above the belt for directing heat downwardly toward saidbelt, a gas inlet for produced reduction gas in the upper part of eachof said hoods above the belt between it and said burner, a gas outletfor produced reduction gas in the lower part of the heating hood belowthe belt, means for dedusting and purifying S0 containing produced gas,gas conduit means connecting said gas outlet of the first heating hood(in the direction of the movement of the conveying belt) to saiddedusting and purifying means, the gas outlets of the second and thirdheating hoods communicating with the produced reduction gas inlets ofthe said heating hoods, means for introducing S0 containing material tobe reduced on to said conveying belt in front of the first of said hoodsfor passage on said belt through said hoods, means for withdrawing thespent $0,; material from the conveying belt behind the last of saidthree hoods, and means connecting said withdrawal means with air supplymeans whereby the heat of said spent material can be utilized to heatsaid air.

4. A device for manufacturing sulfur dioxide by the reduction ofsulfates, comprising an endless conveying belt, three successivelyarranged heating hoods positioned to partially surround the conveyingbelt and to substantially completely surround a portion of belt travel,each of said heating hoods being equipped with a burner in the upperpart thereof above the belt for directing heat downwardly toward saidbelt, a gas inlet for produced reduction gas in the upper part of eachof said hoods above the belt between it and said burner, a gas outletfor produced reduction gas in the lower part of the heating hood belowthe belt, means for drying S0 containing produced gas containing moistsulfate granules, means for dedusting and purifying SO containingproduced gas, gas conduit means connecting said gas outlet of the firstheating hood (in the direction of the movement of the conveying belt) tosaid means for drying and dedusting and purifying, the gas outlets ofthe second and third heating hoods communicating with the producedreduction gas inlets of the preceding heating hood, means forintroducing S0 containing material to be reduced on to said conveyingbelt in front of the first of said hoods for passage on said beltthrough said hoods, means for withdrawing the spent $0,, material fromthe conveying belt behind the last of said three hoods, and meansconnecting said withdrawal means with air supply means whereby the heatof said spent material can be utilized to heat said air.

References Cited in the file of this patent UNITED STATES PATENTS1,926,032 Bunce et a1 Sept. 12, 1933 2,252,279 Zirngibl Aug. 12, 19412,750,274 Lellep June 12, 1956 UNITED STATES PATENT OFFICE CERTIFICATEOF CORRECTION Patent No. 3 129,063 April 14 196 Hans Zirngibl It ishereby certified that error appears in the above numbered patentrequiring correction and tha,t the said Letters Patent should read ascorrected below.

Column 2, line 49, for "zone II read zone III column 3, line .5 after"well" insert as column 4, line 74, after "S0 strike out the comma; line75, for "materials" read material Signed and sealed this llth day ofAugust 1964.

(SEAL) Altest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. A DEVICE FOR MANUFACTURING SULFUR DIOXIDE BY THE REDUCTION OFSULFATES, COMPRISING AN ENDLESS CONVEYING BELT, THREE SUCCESSIVELYARRANGED HEATING HOODS POSITIONED TO PARTIALLY SURROUND THE CONVEYINGBELT AND TO SUBSTANTIALLY COMPLETELY SURROUND A PORTION OF BELT TRAVEL,EACH OF SAID HOODS BEING EQUIPPED WITH A BURNER IN THE UPPER PARTTHEREOF ABOVE THE BELT FOR DIRECTING HEAT DOWNWARDLY TOWARD SAID BELT, AGAS INLET FOR PRODUCED REDUCTION GAS IN THE UPPER PART OF EACH OF SAIDHOODS ABOVE THE BELT BETWEEN IT AND SAID BURNER, A GAS OUTLET FORPRODUCED REDUCTION GAS IN THE LOWER PART OF THE HEATING HOOD BELOW THEBELT, MEANS FOR DEDUSTING AND PURIFYING SO2 CONTAINING PRODUCED GAS, GASCONDUIT MEANS CONNECTING SAID GAS OUTLET OF THE FIRST HEATING HOOD (INTHE DIRECTION OF THE MOVEMENT OF THE CONVEYING BELT) TO SAID DEDUSTINGAND PURIFYING MEANS, THE GAS OUTLETS